1. Field of Invention
The present invention relates generally to viscosity measurements and specifically to improvements to an orbiting object viscometer in the areas of extending the range of such a device to lower viscosity fluids and improving the accuracy of the measurements.
2. Description of Prior Art
The accurate measurement of the viscosity of a fluid is important in a variety of commercial and scientific endeavors. Accordingly, the orbiting object viscometer was developed with the goal of making a viscosity measurement that can be done quickly and which produces accurate and repeatable results for fluids having a wide range of viscosities.
The orbiting object viscometer disclosed in U.S. Pat. No. 5,394,739 measures viscosity by magnetically propelling a magnetic object through a fluid in an orbital pattern. By controlling the magnetic drive parameters and by measuring the resulting behavior of the magnetic object in the fluid and the fluid temperature, accurate and repeatable viscosity values may be calculated. However, when measuring low viscosity fluids, whirlpooling in the fluid causes gross inaccuracies in the calculated results. In addition, measuring fluid temperature through the wall of the receptacle containing the fluid adds variance to the results due to self-heating of the temperature sensor by the measurement apparatus.
A whirlpool reduction device is disclosed in U.S. Pat. No. 5,232,246. This device reduces whirlpooling in fluid entering a drain pipe for the purpose of increasing fluid flow through the drain pipe. The baffles described in patent `246 are not adaptable to the viscosity measurement application for several reasons. The forces causing whirlpools in the two applications are different so the design of the baffles must be different due to differing requirements. The viscosity measurement application has no fluid outflow so that the design and positioning of baffles in the two applications are completely different. In addition, the baffles disclosed in patent `246 are not readily removeable.
What is needed then, is a device that may be used with an orbiting object viscometer, that reduces whirlpooling in low viscosity fluids and provides accurate fluid temperature measurements for use in the viscosity calculations and which is easily removable so that the inherent qualities of the orbiting object viscometer, such as rapid viscosity testing, are maintained.